Added github packages (#58)

        uses: docker/setup-buildx-action@v2

      - name: Build and push Docker image

        if: ${{ startsWith(github.ref, 'refs/tags/*') }}

        uses: docker/build-push-action@v3

        with:

          context: .

          labels: ${{ steps.meta.outputs.labels }}

      - name: Build and push Docker image slim

        if: ${{ startsWith(github.ref, 'refs/tags/*') }}

        uses: docker/build-push-action@v3

        with:

          context: .

For example, in the folder that has your source code, `.spec` file and `requirements.txt`:

```console

```zsh

docker run -v "$(pwd):/src/" batonogov/pyinstaller-windows

```

or

```zsh

docker run -v "$(pwd):/src/" ghcr.io/batonogov/pyinstaller-windows

```

will build your PyInstaller project into `dist/`. The `.exe` file will have the same name as your `.spec` file.

```console

```zsh

docker run -v "$(pwd):/src/" batonogov/pyinstaller-linux

```

or

```zsh

docker run -v "$(pwd):/src/" ghcr.io/batonogov/pyinstaller-linux

```

will build your PyInstaller project into `dist/`. The binary will have the same name as your `.spec` file.

### How do I specify the spec file from which the executable should be build?

You'll need to pass an environment variable called `SPECFILE` with the path (relative or absoulte) to your spec file, like so:

```console

```zsh

docker run -v "$(pwd):/src/" -e SPECFILE=./main-nogui.spec batonogov/pyinstaller-linux

```

You'll need to supply a custom command to Docker to install system pacakges. Something like:

```console

```zsh

docker run -v "$(pwd):/src/" --entrypoint /bin/sh batonogov/pyinstaller-linux -c "apt update -y && apt install -y wget && /entrypoint.sh"

```